Dean L. Olson

High-Resolution Microcoil 1H-NMR for Mass-Limited, Nanoliter-Volume Samples

High-resolution, proton nuclear magnetic resonance (NMR) spectra of 5-nanoliter samples have been obtained with much higher mass sensitivity [signal-to-noise ratio (S/N) per micromole] than with traditional methods. Arginine and sucrose show a mean sensitivity enhancement of 130 compared to 278-microliter samples run in a 5-millimeter tube in a conventional, commercial probe. This can reduce data acquisition time by a factor of >16,000 or reduce the needed sample mass by a factor of about 130. A linewidth of 0.6 hertz was achieved on a 300-megahertz spectrometer by matching the magnetic susceptibility of the medium that surrounds the detection cell to that of the copper coil. For sucrose, the limit of detection (defined at S/N = 3) was 19 nanograms (56 picomoles) for a 1-minute data acquisition. This technique should prove useful with mass-limited samples and for use as a detector in capillary separations.

Using microcontact printing to fabricate microcoils on capillaries for high resolution proton nuclear magnetic resonance on nanoliter volumes

This letter describes a method for producing conducting microcoils for high resolution proton nuclear magnetic resonance (1H-NMR) spectroscopy on nanoliter volumes. This technique uses microcontact printing and electroplating to form coils on microcapillaries. Nuclear magnetic resonance spectra collected using these microcoils, have linewidths less than 1 Hz for model compounds and a limit of detection (signal-to-noise ratio=3) for ethylbenzene of 2.6 nmol in 13 min.

The peroxidase—NADH biochemical oscillator: experimental system, control variables, and oxygen mass transport

Abstract Experimental control variables are defined and characterized to provide good reproducibility of oscillatory behavior, and allow other investigators to perform additional studies under consistently defined conditions. Fifteen variables are recognized and described. Oxygen mass transport has a large effect on the overall appearance of the oscillation, and is quantitatively related to stirring and several other variables. These conditions combine to yield a single, experimentally measurable oxygen mass-transport constant. Stirring is controlled with precision motor which is used to explore the mass-transport constant and mixing time as a function of stirrer rotation rate. Oscillatory behavior is examined under identical conditions with and without the modifiers Methylene Blue and 2,4-dichlorophenol (DCP). Omission of DCP from the system does not appreciably change oscillatory behavior under the specified conditions. Slightly damped oscillations are maintained for six hours. The acidic degradation of NADH is significantly affected by illumination from the deuterium lamp used in UV—visible absorption measurements. The importance and value of an analytical approach to this complex system is emphasized throughout.

Multiplexed NMR: an automated CapNMR dual-sample probe.

A new generation of microscale, nuclear magnetic resonance (CapNMR) probe technology employs two independent detection elements to accommodate two samples simultaneously. Each detection element in the dual-sample CapNMR probe (DSP) delivers the same spectral resolution and S/N as in a CapNMR probe configured to accommodate one sample at a time. A high degree of electrical isolation allows the DSP to be used in a variety of data acquisition modes. Both samples are shimmed simultaneously to achieve high spectral resolution for simultaneous data acquisition, or alternatively, a flowcell-specific shim set is readily called via spectrometer subroutines to enable acquisition from one sample while the other is being loaded. An automation system accommodates loading of two samples via dual injection ports on an autosampler and two completely independent flowpaths leading to dedicated flowcells in the DSP probe.

Analytical Chemistry of Nonlinear Systems

Analytical methods for characterizing complex, nonlinear chemical systems are reviewed. Emphasis is on those aspects of systems which make their characterization more difficult than just measuring concentrations or simple reaction rates. Examples include phase transitions, oscillating chemical reactions, laser fluctuations, and electrochemical oscillations. Data reduction algorithms specific to such systems are described.

Theoretical investigation of the peroxidase-oxidase chemical oscillator for quantitative enzyme analysis

Abstract The theoretical basis for quantitative enzyme determinations by using the features of chemical oscillations is developed. An existing model of the peroxidase-oxidase chemical oscillator, consisting of the enzyme horseradish peroxidase, oxygen and reduced nicotinamide adenine dinucleotide (NADH), is modified to include a competing (analyte) reaction. The competitive effect between the analyte and the peroxidase on the observed periodic and chaotic oscillations forms the basis of the modified model. Corresponding differential equations are numerically integrated to produce plots of dissolved oxygen concentration vs. time. The calculated oscillatory oxygen transient shows a sensitive dependence on the analyte concentration. Utilizing the property of period doubling, a theoretical calibration graph can be generated for the determination of an analyte enzyme concentration. Special properties of the technique offer a potential combination of wide dynamic range and selectable precision. This demonstrates that the oscillator should prove experimentally useful for quantitative analysis.

Peroxidase-oxidase oscillator revisited with rigorous control of reaction conditions

The peroxidase-oxidase system is the only in vitro single-enzyme reaction which has been shown to oscillate chaotically. Difficulties in reproducing literature results have led to careful attempts to specify conditions for reproducing experimental parameters. Progress in specifying reaction conditions is reported. Parameters which require further elucidation before control can be adequately achieved are also specified.